ok i tried to search around for an answer to this question, but

my drivers side window is stuck up, so i pulled the door panel, removed the regulator and the motor, then i plugged in the motor by itself and turned the key, the motor is fine in both directions, then i reattached the regulator to the motor, both still outside the door frame for the test

the regulator moves back and forth freely, on the down stroke it stops when the rubber bump stop hits the metal, which is fine i guess that is so that the window doesn't go too far down into the door frame, but on the up stroke the regulator moves all the way up and the last gear tooth gets jammed in the gear on the motor....then it wont go back down or even budge at all anymore

if i take the regulator off and put it back on then everything works again unless i raise it up all the way and the gear jams again, etc.

upon inspection, it doesn't appear that the gear teeth on either the regulator or the motor are worn/chipped so i cant tell why they are jamming, should there be a rubber bump stop for the regulator on the up stroke as well?? or is the window itself a stop i.e. when it fully raises up in the door frame obviously it can't go any farther

 

Try another test, roll the window up until it jams. Turn on the interior light to see for current draw. Push down on the switch and if the light dims the motor is trying to work. Check for excessive play in any pivot points and around the gear. If the light doesn't dim the motor isn't contacting and you probably need a new one.

 

i am fairly certain the motor is fine, i took it apart inspected the contacts, its definitely not the original motor so its not too old, and it is a very simply induction motor so there is not much that can fail as far as the internals go...it will raise and lower just fine, over and over again no problem, its ONLY when it gets to the last gear tooth on the regulator, then the gears jam, i can shine a light in between the regulator and motor and clearly see that the last gear tooth has almost "jumped" a tooth on the motor and the two teeth are pinned one against another, but when i take them apart, the last gear tooth looks exactly like every other gear tooth on the regulator and the motor, so i can't imagine that its wear and tear thats causing this, but then again something's gotta give right?

 

Are you sure there's no play? Are all the bolts tight? Can you watch it operate with the door panel off and look for something that's not moving right or popping out of place? I had a problem with a window once where the metal the motor and regulator bolted to would push out when the window reached the top. The inner skin could be weak and deforming.

 

Sounds like a bad gear mesh on the last gear... I would replace the regulator.